Time-Resolved Connection between Starspots and Flares in Nearby Young Solar-type Stars Observed by TESS

Abstract

Superflares are energetic explosions on stellar surface with energies of 10^33-10^36 erg, significantly exceeding those of typical solar flares. While previous studies have suggested that these events are driven by magnetic energy stored in large starspots, the detailed time-resolved relationship between starspot area and flare activity on individual stars has remained unclear. In this paper, we investigate the time evolution of magnetic activity on three representative young solar-type stars (EK Draconis, DS Tucanae A, and V889 Herculis) using $\sim$7 years of photometric data from the Transiting Exoplanet Survey Satellite (TESS). We automatically detected stellar flares and derived the flare frequency, starspot area, and rotational period for each TESS sector covering ~27 days. As a result, we found that the flare frequency and starspot area vary significantly across sectors, although we could not identify any activity-cycle-like pattern. There is a positive correlation between the starspot area and flare occurrence frequency for all three targets and the power-law dependence is consistent among the stars. This result supports the physical picture that superflares on young solar-type stars are powered by magnetic energy stored in large starspots, analogous to solar flares, and that the energy release rate changes as the total stored magnetic energy varies. Furthermore, from the analysis of EK Draconis, we find a possible dependence of starspot area on rotation period, which may suggest that large starspots preferentially form at mid-latitudes. These findings demonstrate that the magnetic activity mechanisms established for the Sun extend to the extreme magnetic activity observed on young active stars.